Hydrotreating and aromatic saturation process with integral intermediate hydrogen separation and purification

ABSTRACT

An intermediate hydrogen separation and purification system is integrated with a hydrotreating and an aromatic saturation process for the production of relatively lower molecular weight products from a relatively heavy feedstock including sulfur-containing and aromatic-containing hydrocarbon compounds. The integrated process allows the processing of heavy hydrocarbon feedstock having high aromatic and high sulfur contents in a single-stage configuration and the using of noble metal catalyst in the aromatic saturation zone. The integrated process increases the overall catalytic activity and hydrogenation capability to produce superior distillate products.

RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 13/667,746 filed Nov. 2, 2012, which claims thebenefit of U.S. Provisional Patent Application No. 61/555,905 filed Nov.4, 2011, the disclosures of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to hydrotreating and aromatic saturationsystems and method for efficient production of high quality distillatesfrom high sulfur, high aromatic hydrocarbons at existing or newhydrocracking facilities.

2. Description of Related Art

Hydrotreating technology is a well-known prior art where hydrocarbonfeed boiling in the range of from 150° C.-400° C. (302° F.-752° F.) ismixed with hydrogen at a temperature in the range of from 200° C.-500°C. (392° F.-932° F.) and a pressure in the range of from 34 barg-100barg (493 psig-1450 psig) and the mixture is passed over heterogeneousfixed bed catalyst. The contaminants in the hydrocarbon feed, such asthe sulfur, nitrogen, and oxygen compounds, are almost completelyremoved, and any olefins present are saturated, thereby producingproducts that are a mixture of essentially pure paraffins andnaphthenes. Some of the aromatic content is also saturated. Acceptableproduct will meet the ultra low sulfur distillates specifications. Theheterogeneous fixed bed catalyst contains at least one Group VIII metal,and at least one Group VIB metal. Generally, these metals are includedon a support material such as alumina with or without silica or someother promoter.

The desired degree of hydrotreating takes place as the feed is processedover fixed beds of catalyst at elevated hydrogen pressure andtemperature. The amount of catalyst required per volume of feed and thepressure level are set by the quality of the feed and desired products.

When there is a requirement of maximum aromatic saturation, the productfrom the distillate hydrotreating section is then further processed inan aromatic saturation reaction zone. The aromatic saturation ofdistillates is also a well known prior art, where the hydrocarbon feedis again mixed with hydrogen at temperatures in the range of from 200°C.-400° C. (392° F.-752° F.) and a pressure in the range of from 34barg-100 barg (493 psig-1450 psig) and the mixture is passed overheterogeneous fixed bed catalyst. The heterogeneous fixed bed catalystcontains at least one Group VIII noble metal. Generally, these metalsare included on a support material such as alumina with or without acracking acidic component such as an amorphous silica alumina or azeolite. The hydrocarbon feed is converted to higher-value low sulfur,low aromatic products, which are used as transportation fuel and meetthe current Ultra Low sulfur distillate specifications.

The desired degree of aromatic saturation takes place as the essentiallysulfur-free feed is processed over fixed beds of catalyst at elevatedhydrogen pressure and temperature. The amount of catalyst required pervolume of feed and the pressure level are set by the quality of the feedand the desired products.

Traditionally hydrotreating followed by aromatic saturation is carriedout in multiple stages when the processes are combined into a singleunit or carried out with two separate units. As the sulfur and aromaticcontent for a given distillation range in a hydrocarbon feed increases,the quantity of ammonia and hydrogen sulfide present in thehydrotreating zone effluent will also increase. The hydrogen sulfidewill begin to inhibit aromatic saturation, and therefore in order tomeet a high cetane number or smoke point for the particular distillatefraction, further processing is required. Catalytically this is achievedby increasing the hydrogenation function in the second stage—aromaticsaturation zone. Since higher hydrogenation requires the use of noblemetal catalyst which are poisoned by hydrogen sulfide, an intermediatefractionation section to strip out the hydrogen sulfide, ammonia andlight ends is required. The stripped feed is then processed in the sweet(hydrogen sulfide free) second stage where aromatic saturation iscarried out over a noble metal catalyst system followed by thefractionation section to strip out the hydrogen sulfide and light ends.This complicates the overall plant design and increases the amount ofrecycle gas required to achieve the desired targets.

Accordingly, a need exists in the art for improved hydrotreating andaromatic saturation processes operations, particularly for new systemscapable of processing feedstocks with relatively high sulfur andaromatic content, or for existing systems which have been limited bycatalyst activity and distillate selectivity.

SUMMARY OF THE INVENTION

The above objects and further advantages are provided by hereindescribed process. An intermediate hydrogen separation and purificationsystem is integrated with a hydrotreating and an aromatic saturationprocess for the production of relatively lower molecular weight productsfrom a relatively heavy feedstock including sulfur-containing andaromatic-containing hydrocarbon compounds. The integrated process allowsthe processing of heavy hydrocarbon feedstock having high aromatic andhigh sulfur contents in a single-stage configuration and the using ofnoble metal catalyst in the aromatic saturation zone. The integratedprocess increases the overall catalytic activity and hydrogenationcapability to produce superior distillate products.

The integrated hydroprocessing process is for the production ofrelatively lower molecular weight products from a relatively heavyfeedstock including sulfur-containing and aromatic-containinghydrocarbon compounds. The process comprising comprises:

-   -   a. hydrotreating the feedstock with a hydrotreating catalyst in        the presence of hydrogen to produce a hydrotreated effluent        containing a reduced amount of sulfur-containing hydrocarbon        compounds;    -   b. separating the hydrotreated effluent in a high-pressure        separation zone to produce a vapor stream and a hydrocarbon        liquid stream;    -   c. purifying at least a portion of the vapor stream in an        absorption zone in the presence of at least a portion of        relatively heavier components of vapor stream from step (b) to        produce a high purity hydrogen gas stream and a fuel gas stream;    -   d. saturating the aromatic compounds contained in a portion of        the hydrocarbon liquid stream with an aromatic saturation        catalyst in the presence of hydrogen gas to produce an aromatic        saturated effluent, wherein the hydrogen gas includes the high        purity hydrogen gas stream from step (c) along with make-up        hydrogen stream; and    -   e. separating and fractioning the aromatic saturated effluent to        produce one or more overhead gas streams, one or more sour water        streams and overhead and bottom fractioned distillate products.

In certain embodiments, step (b) comprises separating the hydrotreatedeffluent in a hot high-pressure separation zone to produce ahydrotreated gas stream and a hydrotreated liquid stream, and separatingthe hydrotreated gas stream in a cold high-pressure separation zone toproduce a vapor stream, a hydrocarbon liquid stream and a sour waterstream, wherein the relatively heavier components of the vapor streamused in step (c) are derived from further condensation of the heavierfractions in the vapor stream generated from the cold separator andadditional make up provided by the portion of the hydrocarbon liquidstream from the cold high-pressure separation zone.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description will be best understood when read inconjunction with the attached drawings. For the purpose of illustratingthe invention, there are shown in the drawings embodiments which arepresently preferred. It should be understood, however, that theinvention is not limited to the precise arrangements and apparatusshown. In the drawings the same numeral is used to refer to the same orsimilar elements, in which:

FIG. 1 is a process flow diagram of a hydrotreating and aromaticsaturation system integrated with an intermediate hydrogen separationand purification system; and

FIG. 2 is a schematic diagram of an absorption zone.

DETAILED DESCRIPTION OF THE INVENTION

An integrated hydrotreating and aromatic saturation configuration isprovided which incorporates a hydrogen separation zone along withhydrogen purification by absorption. These additional steps are locatedbetween the hydrotreating reaction zone and the aromatic saturationzone. This removes ammonia and hydrogen sulfide from the intermediatereaction effluent, and allows a purified hydrogen stream to berecombined with the liquid streams to be saturated in an essentiallyammonia-free and hydrogen sulfide-free environment.

In particular, and referring now to FIG. 1, a process flow diagram of anintegrated hydroprocessing apparatus 1000 is illustrated. Apparatus 1000includes a hydrotreating zone 100, a first high-pressure separation zone200, an aromatic saturation zone 300, an absorption zone 400, a secondhigh pressure separation zone 500, a flash zone 600, and a fractionationzone 700.

Hydrotreating zone 100 includes a reactor 144 containing an effectivequantity of a suitable hydrotreating catalyst. Reactor 144 includes aninlet for receiving a combined stream 130 including a feedstock stream120 and a hydrogen stream 124 and an inlet for receiving a quenchinghydrogen stream 146. A hydrotreated effluent stream 140 is dischargedfrom an outlet of reactor 144. In certain embodiments a hydrogen gasinlet can be separate from the feed inlet (in addition to the inlet forintroduction of quenching hydrogen).

The first high-pressure separation zone 200 generally includes a hothigh-pressure separation vessel 210 and a cold high-pressure separationvessel 220. Hot high-pressure separation vessel 210 includes an inletfor receiving the hydrotreated effluent 140, an outlet for discharging ahydrotreated gas stream 230 and an outlet for discharging a hydrotreatedliquid stream 240. Stream 230, which includes one or more gases selectedfrom the group comprising hydrogen, methane, ethane, ammonia, hydrogensulfide, C₅+ hydrocarbons, exits the first separation vessel 210.

Cold high-pressure separation vessel 220 includes an inlet in fluidcommunication with separation vessel 210 and for receiving the partiallycondensed hydrotreated gas stream 230, an outlet for discharging a vaporstream 250, an outlet for discharging sour water stream 290 and anoutlet for discharging a hydrocarbon liquid stream 261. Heat exchangersrequired to cool, the hot stream before entering subsequent cold highpressure separator are not shown and their requirements should beunderstood by a person having ordinary skill.

As shown in FIG. 2, absorption zone 400 includes a cross exchanger 410,a chiller 420, a methane absorber column 430, a flash regenerationvessel 440 and a solvent circulation pump 442. Methane absorber column430 includes an inlet for receiving vapor stream 250 from high-pressureseparation zone 200 after cross-exchanger 410 and chiller 420, an inletfor receiving recycle solvent stream 444 from flash regeneration vessel440, an inlet for receiving solvent make-up stream 260, an outlet fordischarging a rich solvent liquid stream 432 and an outlet fordischarging a hydrogen stream 450. In absorption zone 400, stream 250from the cold high pressure separator 220, which is a relatively low H₂purity stream, is counter-currently contacted with a portion ofcondensed hydrocarbon liquids from stream 260 as solvent in the methaneabsorber column 430 to absorb methane and heavier hydrocarbons away fromthe contained hydrogen. Stream 250 is chilled in a heat exchanger 410 bycross-exchanging with a colder, purified, recycled hydrogen stream 450,followed by refrigeration unit 420 where it is cooled to about −20° F.In the absorber column 430, most heavy gases including methane, ethane,propane, butanes, pentanes and heavier gases, are absorbed and separatedfrom the contained hydrogen in stream 250. The rich solvent liquidstream 432 from the bottom of the absorption zone 430 is passed to atleast one flashing stage 440. Through pressure letdown in flash drums,rich solvent stream 432 is separated and a lean liquid solvent stream444 is derived that can be recycled back to the methane absorber column430 using a solvent circulation pump 442. The bulk of the solvent usedfor absorption is primarily the heavier hydrocarbons which are condensedfrom stream 250 after chilling. The hydrocarbon stream 260 is primarilyused as a make-up solvent.

Arrangements similar to absorption zone 400 are shown in U.S. Pat. Nos.6,740,226, 4,740,222, 4,832,718, 5,462,583, 5,546,764 and 5,551, 972,and U.S. Pub. No. 2007/0017851, the disclosures of which are allincorporated by reference herein in their entireties.

As depicted process flow lines in the figures can be referred to asstreams, feeds, products or effluents. Depending upon the ammoniacontent, a water stream (not shown) can be added to stream 230 to removeammonium bisulfide salts. Stream 290 is predominantly sour water thatcan be sent to any suitable destination such as a sour water stripper.The separated vapor from separator 220 leaves through stream 250 andenters the absorption zone 400. The portion 260 from the separator 220liquid hydrocarbon discharge stream 261 is routed to form the absorptionsolvent through solvent make-up stream 260 for the absorption zone 400as discussed above. A hydrocarbon stream 265, which is the remainder ofstream 261 from the separator 220 that is not routed as absorptionsolvent make-up 260, bypasses the aromatic saturation zone 300.

The absorption zone 400 purifies the hydrogen present in stream 250 byabsorbing components heavier than hydrogen with circulating solventcomprising solvent make-up stream 260 to produce a high purity (95-99mol %) hydrogen stream 450 and a fuel gas stream 460 comprisingcomponents heavier than hydrogen as present in stream 250.

The high purity hydrogen stream 450 along with high purity make-uphydrogen stream 204 from manifold “Header B” then combine with liquidstream 240 to form a combined feed 330 to enter the aromatic saturationzone 300.

The aromatic saturation zone 300 includes an aromatic saturation reactor320, which may have single or multiple catalyst beds and receive quenchhydrogen streams in between the beds as simply shown by stream 326.Although only one quench hydrogen stream is shown, it should beunderstood that multiple streams may be provided to the aromaticsaturation reactor 320 depending upon the number of beds. The aromaticsaturation zone 300 can operate at any suitable condition. The effluentstream 340 from the aromatic saturation zone 300 along with the excesshydrocarbon stream 265 from the separator 220 combine to form stream 390which enters the second separation zone 500.

Separation zone 500 includes a separation vessel 510. Heat exchangersare required to cool the hot stream 340 before entering the highpressure separator vessel 510. The high pressure separator drum 510 canprovide an overhead stream 514 comprising hydrogen and methane(predominantly rich in hydrogen), a hydrocarbon stream 530 which entersthe flash zone 600 and a heavy liquid stream 520 which is predominantlysour water that can be sent to any suitable destination such as a sourwater stripper. A water stream (not shown) can be added to the combinedstream 390 to remove ammonium salts.

Flash zone 600 includes a cold low-pressure flash drum 610. Heatexchangers required to cool the hot streams are not shown and theirrequirement should be understood by those of ordinary skill in the art.Typically, the flash drum 610 separates gases from condensed liquids orfrom liquids through pressure let down.

The low pressure cold flash drum 610 provides an overhead stream 614comprising hydrogen and methane (predominantly rich in hydrogen), ahydrocarbon side stream 618 and a bottom stream 620 which ispredominantly sour water that can be sent to any suitable destinationsuch as a sour water stripper. The hydrocarbon liquid side stream 618 isintroduced to the fractionation zone 700.

Generally, the fractionation zone 700 produces a variety of products,and includes an overhead stream 710, and a bottom stream 750. Typically,stream 710 comprises unstabilized naphtha, and the bottom stream 750 isessentially a high quality distillate product that in certainembodiments meets requisite product quality standards such as a highcetane number, a high smoke point and low sulfur content.

The high-pressure separator drum 510 provides an overhead stream 514,which is rich in hydrogen and can be recycled back after compressionthrough recycle hydrogen compressor 680 to produce stream 685, which isrecycled back to the hydrogen manifold “Header A”. The high puritymake-up hydrogen stream 204 from manifold “Header B” can typically befrom a hydrogen generation unit.

The feedstock for present processes and apparatus generally containscomponents boiling in the range of from 150° C.-400° C. (302° F.-752°F.). Usually, these feeds can include straight run gas oil; a crudedistillation unit product, such as light vacuum gas oil; a vacuumdistillation unit product; a thermally cracked gas oil; a visbreakingunit, thermal cracking or coking unit product; light or heavy cycle oil;a fluid catalytic cracking unit product, and light gasoil derived fromtar sands.

In general, the hydrotreating reaction zone can include a hydrotreatingreactor which can have single or multiple catalyst beds and can receivequench hydrogen stream between the beds. Although only one hydrogenquench inlet is shown, it should be understood that the hydrogen streamcan be provided anywhere along the hydrotreating reactor and multiplehydrogen streams may be provided depending upon the number of beds. Thehydrotreating reactor beds typically contain a catalyst having at leastone Group VIII metal, and at least one Group VIB metal. The Group VIIImetal is selected from a group consisting of iron, cobalt, and nickel.The Group VIB metal is selected from a group consisting of molybdenumand tungsten. The Group VIII metal can be present in the amount of about2-20% by weight, and the Group VIB metal can be present in the amount ofabout 1-25% by weight. Generally, these metals are included on a supportmaterial, such as silica or alumina. The operating conditions forhydrotreating reaction zone includes a reaction temperature in the rangeof from 200° C. to 500° C. (392° F. to 932° F.), and a reaction pressurein the range of from 34 barg to 100 barg (493 psig to 1450 psig).

The operating conditions for the hot high-pressure separation zoneincludes a temperature in the range of from 200° C. to 500° C. (392° F.to 932° F.), a pressure in the range of from 30 barg to 100 barg (435psig to 1450 psig). The operating conditions for the cold high-pressureseparation zone includes a temperature in the range of from 60° C. to250° C. (140° F. to 482° F.), a pressure in the range of from 30 barg to100 barg (435 psig to 1450 psig).

In general, the aromatic saturation zone can include an aromaticsaturation reactor which can have single or multiple catalyst beds andcan receive quench hydrogen stream between the beds. Although only onehydrogen quench inlet is shown, it should be understood that thehydrogen stream can be provided anywhere along the aromatic saturationreactor and multiple hydrogen streams may be provided depending upon thenumber of beds. The aromatic saturation reactor beds typically contain acatalyst having at least one Group VIII noble metal. The Group VIIInoble metal is selected from a group comprising platinum, palladium,ruthenium, rhodium, osmium, and iridium. Generally, these metals areincluded on a support material, such as silica or alumina along withacidic component such as amorphous silica alumina or a zeolite. Usually,the Group VIII noble metal can be present in the amount of about 0.2-5%by weight. The operating conditions for aromatic saturation zoneincludes a reaction temperature in the range of from 200° C. to 400° C.(392° F. to 752° F.), and a reaction pressure in the range of from 30barg to 100 barg (435 psig to 1450 psig).

The operating conditions for the separation zone 500 includes atemperature in the range of from 40° C. to 80° C. (104° F. to 176° F.),and a pressure in the range of from 30 barg to 100 barg (435 psig to1450 psig).

The operating conditions for the cold low-pressure flash drum includes atemperature in the range of from 40° C. to 80° C. (104° F. to 176° F.),and a pressure in the range of from 20 barg to 50 barg (290 psig to 725psig).

The operating conditions for the fractionation zone includes atemperature in the range of from 40° C. to 400° C. (104° F. to 752° F.),and a pressure in the range of from 0.05 bar to 20 bar (0.73 psig to 290psig).

Heat transfer equipment, fluid transport equipment and mass transferequipment have not always been shown and their requirement must beunderstood by one skilled in the art.

Distinct advantages are offered by the integrated hydroprocessingapparatus and processes described herein when compared to conventionalhydroprocessing configurations. The integrated process allows theprocessing of heavy hydrocarbon feed having high sulfur and higharomatic contents in a single-stage configuration which allows thereduction of recycle gas in the amount of 20% to 30% by volume comparedto the normal gas flow needed for the conventional flow schemesutilizing two-stage designs. The integrated process also allows theability to not only make ultra low sulfur distillates (ULSD) but alsohigh smoke point kerosene and high cetane diesel when processing highsulfur and high aromatic distillate range feed stock. In addition, theintegrated process allows a reduction in the system pressure because ofhigher hydrogen partial pressure at the hydroprocessing zones due toavailability of high purity hydrogen and thus saving capital cost.

The method and system herein have been described above and in theattached drawings; however, modifications will be apparent to those ofordinary skill in the art and the scope of protection for the inventionis to be defined by the claims that follow.

What is claimed is:
 1. An integrated hydroprocessing process for theproduction of relatively lower molecular weight products from arelatively heavy feedstock including sulfur-containing andaromatic-containing hydrocarbon compounds, the process comprising: a.hydrotreating the feedstock with a hydrotreating catalyst in thepresence of hydrogen to produce a hydrotreated effluent containing areduced amount of sulfur-containing hydrocarbon compounds; b. separatingthe hydrotreated effluent in a high-pressure separation zone to producea vapor stream and a hydrocarbon liquid stream; c. purifying at least aportion of the vapor stream in an absorption zone in the presence of atleast a portion of relatively heavier components of vapor stream fromstep (b) to produce a high purity hydrogen gas stream and a fuel gasstream; d. saturating the aromatic compounds contained in a portion ofthe hydrocarbon liquid stream with an aromatic saturation catalyst inthe presence of hydrogen gas to produce an aromatic saturated effluent,wherein the hydrogen gas includes the high purity hydrogen gas streamfrom step (c) along with make-up hydrogen stream ; and e. separating andfractioning the aromatic saturated effluent to produce one or moreoverhead gas streams, one or more sour water streams and overhead andbottom fractioned distillate products.
 2. The process as in claim 1,where step (b) comprises separating the hydrotreated effluent in a hothigh-pressure separation zone to produce a hydrotreated gas stream and ahydrotreated liquid stream, and separating the hydrotreated gas streamin a cold high-pressure separation zone to produce a vapor stream, ahydrocarbon liquid stream and a sour water stream, wherein therelatively heavier components of the vapor stream used in step (c) arederived from further condensation of the heavier fractions in the vaporstream generated from the cold separator and additional make up providedby the portion of the hydrocarbon liquid stream from the coldhigh-pressure separation zone.
 3. The process as in claim 2, whereinstep (d) comprises saturating the aromatic compounds contained in thehydrotreated liquid stream from the hot high-pressure separation zone.4. The process as in claim 3, wherein step (e) comprises separating thearomatic saturated effluent into an overhead gas stream, a condensedhydrocarbon liquid stream, and a sour water stream; flashing thecondensed hydrocarbon liquid stream from to produce an overhead gasstream, a hydrocarbon liquid side stream and a sour water stream;fractionating the hydrocarbon liquid side stream from step to produce afractioned overhead stream and a fractioned bottom stream; andrecovering the fractioned overhead stream and the fractioned bottomstream as products.